The present invention concerns a composition of adsorbent containing phyllo-alumino silicate containing schistose particles having at least partially a layered structure with substantially parallel layers, whereby they at least for 30 percent by weight consist of 14 xc3x85 phyllo-alumino silicate. The distance between two adjacent structural layers is greater than 5 xcexcm, but less than 100 xcexcm.
The use of berngite as an absorbing alumino sicilate containing schistose material is known. The preparation of this material requires heating at high temperature (600xc2x0 C. and more) in a furnace. Such heating requires not only large expenditures, but is also ecologically harmful, because harmful substances and gases are released during heating. Moreover, such heating is very expensive as regards investments (furnace) and as regards the use of fuels. Beringite has an absorption power which is limited.
In the state of the art, there is no mention of the particular effect of the application of specific aluminum particles with a minimum specific surface area of 100 m2/g which are attached onto specific 14 xc3x85 phyllo-alumino silicate, neither of a maximum length or diameter of the aluminum particles, nor of a minimum percentage by weight of aluminum containing di-octahedric layers in the 14 xc3x85 phyllo-alumino silicate, nor of the distance between two adjacent di-octahedric layers. In the state of the art, there is neither mention of a synergy at relatively low pH (6.5-8.5) between OH groups on the micronised and also etched aluminum plates or particles and the absorption thereof on the heavy metals, which in this way causes a flocculation.
This use of micronised and etched metallic plates or flakes is not limited to aluminum, but is also valid for all other tri- and bivalent metal particles and their alloys, as well as their mixtures (Alxe2x80x94Cu, Alxe2x80x94Cr, Cr, Cu, Crxe2x80x94Cu, Ni, Nixe2x80x94Fe, Fexe2x80x94Cr, etc.).
It has now been found that specific alumino silicate containing schistose particles, which are provided with specific impurities (such as Me, Cu, Zn, Pb, Ni, Cd, Cr) in the crystal lattice, possess excellent sorption efficiency. The invention thus concerns a composition of adsorbent containing alumino silicate containing schistose particles which at least partially have a layered structure, whereby, at least for 30 percent by weight of the alumino silicate containing schistose particles, the distance between two structurally adjacent layers is greater than 5 xcexcm, but less than 100 xcexcm.
The particles consist at least partially of aluminum containing di-octahedric layers. Preferably, at least 25 percent by weight of the particles consist of aluminum containing di-octahedric layers. The particles are provided on their inner and outer layers of metallic particles or flakes or spangles (aluminum, iron, chromium, iron-chromium, Ni, Crxe2x80x94Ni, Alxe2x80x94Ni, Alxe2x80x94Cu, Alxe2x80x94Cr) with metallic hydroxide ions (hydroxylation), whereby these metallic particles are at least partially bound onto and between two structurally adjacent layers by adhesion or other physicochemical forces. These flakes preferably form a substantially complete metallic layer onto the phyllo-alumino silicate particles. At least 50 percent by weight of the metallic flat particles or flakes have a maximum length or diameter between 6 and 60 xcexcm, a thickness of a few xcexcm (2 to 5), and a specific surface area greater than 100 m2/g, due to the size and the etching.
In the present context, the specific surface area of particles is determined by nitrogen adsorption using the B.E.T. (Brunauer, Emmet, Teller) method, as simplified by Haub and Dxc3xcmbgen. The apparatus used is the Strxc3x6hlein Area-Meter II, available from Strxc3x6hlein A. G. in Germany, the manual of which refers to the simplified B.E.T. method.
Alumino silicate containing schistose particles of the sorbent according to the invention are mainly 14 xc3x85 di-octahedric alumino silicate with an adequate microporosity and capillarity, onto which and within which hydrolysed metallic particles with OHxe2x88x92 ions (aluminum hydroxide) are physically and chemically adsorbed or bound. The alumino silicate containing schistose particles can contain up to 40,000 ppm of metallic particles. The sorbent contains for example 5,000 to 20,000 ppm of metallic particles or flakes.
The metallic particles or flakes are preferably aluminum or aluminum oxide particles, which after hydroxylation are provided with aluminum hydroxide.
Preferably, at least for 30 percent by weight of the alumino silicate containing schistose particles, the distance between two structurally adjacent layers is greater than 10 xcexcm, but less than 100 xcexcm, for example greater than 5 xcexcm but less than 10 xcexcm. Still better is an average distance between two structurally adjacent layers of the alumino silicate containing schistose particles of about 10-20 xcexcm, while the maximum average length of the metallic (preferably aluminum or aluminum oxide) flakes is between 10 and 60 xcexcm. The metallic flakes are preferably etched particles with a specific surface area greater than 100 m2/g. This specific surface area is preferably greater than 150 m2/g, for example 200 to 500 m2/g. These metallic flakes preferably contain one or several open cavities with an irregular circumference. The diameter of a cavity ( [surface of the cavity/xcfx80]1/2) is preferably at least two times larger than the diameter of the flakes. The thickness of the walls of the particles around the cavity is for example less than 3 xcexcm.
According to an embodiment, at least 50 percent by weight of the structure of weathered alumino silicate containing schistose particles consist of a 14 xc3x85 aluminum containing di-octahedric structure. The degree of weathering is indicated by the substitution of magnesium by aluminum which should at least amount to more than 50%.
Compositions of the adsorbent according to the invention, which are very suitable for the sorption and the fixation of heavy metals, carry aluminum hydroxide ions which are bound to one or several of the following elements: Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn. It has been found that the epitaxy or in situ growth of the precipitated heavy metals preferably occurs on the di-octahedric alumino silicate crystal surfaces, on the sites where in the crystal lattice analogous or the same heavy metals occur as natural or artificial impurities, such as Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn.
At least 50 percent by weight of the aluminum or aluminium oxide particles with hydroxyl ions preferably possess a specific surface area greater than 150 m2/g.
Preferably, in the alumino silicate containing schistose particles, 20 percent by weight of aluminum chlorite is present. For example, in the absorbing composition, at least 50 percent by weight of the alumino silicate containing particles may be aluminum chlorite.
According to an advantageous embodiment, at least 50 percent by weight of the alumino silicate containing schistose particles have a diameter greater than 500 xcexcm. Preferably, the diameter of the particles is less than 2,000 xcexcm.
According to an embodiment, the sorbent comprises porous particles, which show a weak acid reaction (with a pKa between 4 and 7).
According to another embodiment, the sorbent does or does not comprise adsorbed calcium and/or magnesium containing fertiliser, nitrate fertiliser, phosphate fertiliser, or a mixture thereof.
A composition according to the invention, which is suitable for the fixation of one or several heavy metals, contains di-octahedric phyllo-alumino silicate with as natural impurities in the crystal lattice a total of at least 500 ppm of one or several elements of the following series: Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn.
The sorbent may also be mixed with active carbon for specific applications (removal of Hg, etc.).
Preferably, the alumino silicate containing schistose particles for at least 20 percent by weight consist of weathered or not weathered mica or for at least 20 percent by weight of weathered vermiculite.
The particles of the sorbent, according to the intended use, may be smaller or greater than 200 xcexcm in diameter. The sorbent for examples carries on the free surface 5,000 through 40,000 ppm, preferably 7,550 through 20,000 ppm of hydrolysed metallic flakes, in particular hydrolysed aluminum flakes. Particles of the sorbent smaller than 200 xcexcm in diameter are very suitable for soil sanitation, whereas particles greater than 500 xcexcm in diameter are very suitable for water cleanup.
In order to obtain particles with the desired range of diameters, dry sieving, by means of a sieve or sieves with openings having the appropriate diameter(s), may be used.
According to an embodiment, the Al/Si weight ratio of the alumino silicate containing schistose particles is higher than 1/4, but preferably less than 0.8. This ratio may optionally be changed by addition of aluminum and or silicium (in liquid form or solid formxe2x80x94etched flakes of Al2O3, SiO2 particles).
The metallic etched flakes, such as the aluminum flakes, are preferably bound by adhesion forces or by other physicochemical forces to the alumino silicate containing schistose material.
In order to prevent swelling upon the filtration of the sorbent, stronger binding forces can be used. For example, a binding mass with an Al/Si weight ratio of 0.3 to 1, preferably from 0.3 to 0.4, may be used. This mass further consists of, for example, 25% of Al2O3, 42% of SiO2, 30% of CaO and/or MgO, and 3% of Fe2O3. After this treatment, around and partially in the alumino silicate particles, a strong porous coating (containing aluminum hydroxyde) having a high buffering power at a pH of about 8-10.5 and a pressure strength of 10-20 N/mm2, is obtained. The pressure strength is measured using a strain-stress apparatus, type T50001 with digital display, obtainable from J.J. LLOYD INSTRUMENTS Ltd., in Southampton, England. During the measurement, the cross head progresses with a speed of 6 mm per minute.
The invention also concerns a process for the absorption and fixation of one or several of the following elements Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn which are present in a medium (liquid medium, soil, etc.) to which a sorbent according to the invention is added. The composition according to the invention is suitable for the simultaneous fixing of nonferrous heavy metals. Preferably prior to, or during the addition of the newly described sorbent to the medium, the pH of the medium is adjusted between 4 and 13, preferably between 4.5 and 8. Because of the natural presence of CO2, or the artificial addition thereof, a solid precipitate of alumino-heavy metal complex on the alumino silicate containing schistose particles may be observed, and/or onto the aluminum flakes bound thereto. For example, in a polluted Ni solution, thus a Ni containing dark precipitate is formed. In the process according to the invention, the absorption process is little or not influenced by temperature fluctuations between about xe2x88x921xc2x0 C. (about 0xc2x0 C.) to 75xc2x0 C., preferably between 5 and 50xc2x0 C. The reaction rate of the absorption in the process according to the invention is higher than when using beringite. In examples in which Ni and Pb have to be removed from a polluted water, contact times of 3 to 8 minutes suffice for a sorbent according to the invention to obtain a fairly complete absorption of these heavy metals. In order to obtain the same absorption using beringite, contact times of more than 20 minutes can still be insufficient. With the sorbent according to the invention, after a contact time of 8 minutes, upon filtration removal of heavy metals in excess of 98 and even 99% is observed. For the highly toxic Cd and other elements, the content in the filtrate can successfully be brought down to the limit of measurability (0.001 ppm).
According to an embodiment of the process, one or several heavy metals may be removed in a very efficient way from a polluted aqueous solution. In order to achieve this, the described composition of the sorbent is sufficient to remove the heavy metals considered.
According to an embodiment of the process according to the invention, before, during or after the addition of the new sorbent to the medium, Fe(OH)3 and/or (NH4)2HPO4 and/or sodium carbonate is added to the medium, especially to increase the number of bed volumes to be purified.
The process is highly suitable for the sanitation or purification or decontamination of aqueous solutions or suspensions containing one or several sulphates or chloride salts of the following elements Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn.
According to a specific embodiment of the process according to the invention, the aqueous solution is percolated through sorbent aggregates. Preferably, these aggregates are mixed with the above mentioned binding mass. Also by means of the sorbent, a polluted suspension and/or a polluted aqueous solution may be purified, either or not with application of regular agitation.
Subsequently, the aqueous solution or suspension is treated (for example by filtration, precipitation, decantation, . . . ) in order to separate the solid particles (loaded sorbents) from the aqueous solution.
According to a specific embodiment, which is suitable for the treatment of aqueous solutions containing one or several heavy metals, the aqueous solution is percolated through one or several bed volumes of sorbent aggregates.
In view of the efficiency of the newly described sorbent (finely sieved particles), soil may be cleaned up by spreading the sorbent onto it, and raking or ploughing it in, for example up to a depth varying from 10 through 50 cm. It should be ensured, that the sorbent is equally distributed in the soil stratum. The treated soil may then be planted with fir trees, so that the pH of the ground is maintained between 4.5 and 6.5. Also sanitations may be performed by repeating the treatment once or several times, so that after 3 to 4 years, normal crops can be grown on a cleaned up soil. The composition according to the invention may also be used for the sanitation of ponds and lakes located in the vicinity of zinc and lead processing industry. For example, 0.5 to 50 g of sorbent is added per liter in these ponds or lakes.
The invention further also concerns a process for the preparation of a sorbent according to the invention. In this process,
a) alumino silicate containing schistose particles having at least partially a layered structure, whereby at least for 30 percent by weight of the alumino silicate containing schistose particles, the distance between two structurally adjacent layers is greater than 5 xcexcm, but less than 100 xcexcm, and whereby at least 25 percent by weight of the alumino silicate containing schistose particles consist of aluminum containing 14 xc3x85 di-octahedric layers, and
b) metallic flakes or particles (preferably aluminum or aluminum oxide flakes) having a maximum length or diameter between 6 xcexcm and 60 xcexcm, with a thickness of 2 to 5 xcexcm and with a specific surface area of at least 100 m2/ g
are mixed. Subsequently, providing contact with water, a hydrolysis occurs on the metallic flakes. Onto the free surface of the metallic flakes, OHxe2x88x92 ions are formed. This hydrolysis is preferably performed in an aqueous solution with a pH of 4.5 to 8 (preferably of 5 to 6.5). The use of aluminum particles with a maximum diameter below 5 xcexcm is disadvantageous, as these particles to a large extent disappear within the porosity of the carrier material (alumino silicate). In this way, the porosity of the particles is lowered, and the internally formed ions are less efficiently provided for the precipitation, nucleation and epitaxial crystal growth. Aluminium particles with a maximum length or diameter greater than 60 xcexcm or with a thickness greater than 6 xcexcm are also disadvantageous, because the thus formed OHxe2x88x92 ions are insufficiently physically or mechanically bound onto the alumino silicate containing particles.
The hydrolysis of the metallic aluminum particles preferably occurs in an aqueous suspension containing Al2O3, SiO2, CaO and/or MgO, and further also preferably Fe2O3, in order to form a binding porous mass or coating in and around the particles. Preferably, this mass has an Al/Si weight ratio of 0.3 to 1, preferably of 0.3 to 0.4. After this treatment, in and around the phyllo-alumino silicate particles a strong porous mass (containing aluminum hydroxide) is obtained, having a high buffering power, for example at about a pH of 8-10.5, and a pressure strength of 10-20 N/mm2.
The process according to the invention is preferably performed at temperatures below 50xc2x0 C., whereby the alumino silicate containing sorbent particles are not subjected to heating. Such heating leads to an oxidation of the components with an Eh value up to 80-100 millivolts or more, which inhibits the precipitation of heavy metal complexes. In the process according to the invention, the normal reduction circumstances of the schists (Eh value of 20 to 30 millivolts) is left unaltered.
Preferably, the sorbent particles are hydrolysed with an aluminum or aluminum oxide external layer in the presence of at least one of the following elements Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn in order to obtain aluminum hydroxide ions, which interreact with at least one of the following elements Fe, Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn.
Due to the selection of the alumino silicate schists made, the crystal lattice has one or several heavy metals as impurities, such as Cr, Cu, Ni, Co, Sr, Cd, Pb, Zn or Mn. These elements serve as seeds and centre of attraction for equal elements which are precipitated from the water, and by which the epitaxy or in situ growth of the precipitated heavy metals may develop well.
According to an embodiment, the metallic flakes or particles with metallic hydroxide ions are put into a solution with a weak acid or acids with a pKa between 4 and 7, to control the hydrolysis.
As the hydrolysis may take place in the water to be cleaned, the invention also concerns a composition of adsorbent containing alumino silicate containing schistose particles having at least partially a layered structure, whereby at least for 30 percent by weight of the alumino silicate containing schistose particles, the distance between two structurally adjacent layers is greater than 5 xcexcm, but less than 100 xcexcm. At least 25 percent by weight of the particles consist of aluminum containing di-octahedric layers. The inner or outer layer of the phyllo-alumino silicate particles is provided with metallic particles or flakes or spangles (aluminum, iron, chromium, iron-chromium, Ni, Crxe2x80x94Ni, Alxe2x80x94Ni, Alxe2x80x94Cu, Alxe2x80x94Cr), whereby these metallic particles are at least partially bound onto and between two structurally adjacent layers by adhesion or other physicochemical forces. At least 50 percent by weight of the metallic flat particles or flakes have a maximum length or diameter between 6 and 60 xcexcm, a thickness of a few xcexcm (2 to 5), and a specific surface area greater than 100 m2/g, due to the size and the etching.